Transport systems with a linear motor drive, i.e. linear transport systems, are well known in the state of the art. The most prominent example is a high-speed passenger train on the basis of magnetic levitation technology. Transport systems with a linear motor drive, however, are also used in many industrial fields (e.g., for individual transport of piece items within production lines).
For example a linear transport system with a plurality of magnetic rotors for the transport of bottles in a container treatment device is described in the DE 10 2013 218 389 A1. In this context, the rotors that transport the bottles move in a way as to be driven by the magnetic interaction between a secondary part of the rotors that carry a permanent magnet and/or electromagnets and two long stators along two guiding rails that are guided in parallel and that are connected to the respective long stator. The rotors are thereby supported on the guiding rails and generally have a chassis with a rectangular form on the plane of the roller bearings, wherein roller pairs, which are only spaced slightly from one another, encroach on the respective guiding rail in the longitudinal direction of the rotors.
In practice, there are contradictory requirements for the design of the rotors. On one hand, the rotors should have an extension as small as possible in the longitudinal direction, i.e. in the movement direction, so that the distance of the containers or objects to be transported by them, i.e. the transport spacing, is as small as possible in the container flow to be formed and hence that the throughput of containers per time unit of a container treatment facility that uses the transport system can be as high as possible. If each rotor transports exactly one container, there will for example be the minimal attainable spacing if successive rotors drive in a way as to be in contact with one another. This minimal attainable spacing therefore corresponds to the maximum longitudinal extension of the rotors, provided that the containers are smaller than the rotors. Likewise, a small longitudinal extension of the rotors is desirable to be able to input small containers in the piled-up state at a transition point by a transport belt.
Conversely, it is desirable to form the rotors as long as possible in order to reduce wear and stress of the bearing elements, in general of the rollers. In addition, the rollers for a long rotor can be formed smaller than for a short rotor. Alternatively, the rotor can take on a higher load if the bearing elements are dimensioned identically.
In the transport systems known in the state of the art, the guiding rails for the bearing elements of the rotors and the long stators of the linear motors extend in parallel to one another. This is also the case in the area of curves, which is generally no problem for rotors in which the rollers along the respective guiding rail are located at a close distance to one another. However, if we seek to equip the rotors with an increased roller spacing in the longitudinal direction for the reasons mentioned above, the geometric proportions of the magnetic drive will change when driving into curves. Due to the inevitable overlaps, the distance between the secondary part of the rotor and the long stator is increased or reduced, depending on whether the curve is an inside or an outside curve. For functional reasons, however, it is desirable that this distance, and/or more specifically the width of the air gap between the magnets of the secondary part and the magnets, i.e. the coils and/or the iron cores of the coils, of the long stator remains constant during the entire ride because a change of this distance would lead to a significant change of the normal and propulsion forces onto the rotor.